Prior art tongue switch assemblies typically involve a single cast piece that includes flangeways, turnout rail segments and closure rail segments, with the principal separate and removable component being the tongue itself. This arrangement gives rise to certain difficulties. Movement of the tongue tends to wear the underlying surface of the assembly. If the wear becomes such that replacement is required, the entire assembly must be replaced.
One method used to connect the tongue to the underlying assembly is by pivoting it about the heel end (see e.g. U.S. Pat. No. 2,377,273 to Siebert). The pivot point consists of a pin extending downward from the tongue and inserted into a recess in the underlying switch base. A bearing surface is sometimes provided between the pin and the recess (see, e.g. U.S. Pat. No. 1,853,981 to Kimmel) to protect the pin or pivot from the impact and shearing forces it experiences when the train wheels pass over it. However, this bearing surface must be properly lubricated to ensure that the tongue moves smoothly and the entire pivot point must also be protected from the elements to ensure that it continues to function properly. It is therefore known to provide a cover plate, often integral to the wheel path, over the tongue heel to protect the pivot point (see e.g. U.S. Pat. No. 625,458 to Nichols). However, passage of the train over the cover plate tends to wear the cover plate and its hold down points.
Motion of the tongue between its two extreme positions requires a switch machine powerful enough to overcome not only the weight of the tongue itself, but also the frictional forces between the tongue and the underlying surface. It is therefore important to minimize this friction. One approach to reducing friction is to use lubricants spread on the slide plate surface. However, the application and replacement of lubricant is costly and time-consuming. It is also known to provide friction-reducing coverings for the slide surface. These coverings can take the form of a spray-coated ceramic, as in U.S. Pat. No. 4,890,804 to Teramoto, or a self-lubricating plastic insert, as in U.S. Pat. No. 5,127,613 to Germann. However, once the coating has worn away or if the slide surface itself is damaged, the entire assembly must be replaced. Another approach is to use a slide chair or roller assembly to carry the tongue. Slide chair or roller assemblies are more complex than simply applying lubricant, and they must frequently be replaced.
Tongue switch assemblies are often used in embedded or paved track systems (see e.g. U.S. Pat. No. 4,251,042 to Frank). In such systems, the tongue switch assembly is embedded in pavement or concrete, making it difficult to replace or maintain the switch.
Embedded tongue switch assemblies also present an additional problem when used in association with electric locomotives. In such cases, a current-carrying conductor rail typically lies inside an embedded trough that runs parallel to the load-bearing rails. A collector extends from the train to make physical contact with the conductor rail. When the switch is thrown, the conductor rail must be repositioned and reoriented to accommodate the new position of the tongue so that a consistent distance is maintained between the rail and the collector. It has been proposed to accomplish this by enclosing the conductor rail in a movable inner box assembly enclosed within a switchbox. Movement of the inner box assembly and its associated conductor rail is actuated by means of a lever arm mounted vertically between the switchbox and the load-bearing rail, with an arm extending the lever arm to the underside of the inner box assembly. However, such location of the lever arm would present particular difficulties in maintaining or replacing the lever arm. Access to the lever arm is difficult in that the entire switchbox must be disengaged and removed from its embedded position along with portions of the trackwork or the tongue switch assembly. In addition, it has been proposed to cast the outer shell of the movable switchbox as a single aluminum piece for ease of installation, but this would make it relatively weak and difficult to manufacture.
It is an object of the present invention to provide a tongue switch assembly that is easy to maintain, repair and replace as necessary, even in embedded or paved tracks.
It is a further object of the present invention to simplify the maintenance required for the wear surface of the tongue switch assembly by eliminating the need for lubricants.
It is yet a further object of the present invention to provide a pivot retainer for the tongue which is not subject to the impact and increased wear caused by passing trains.
It is another object of the present invention to provide a novel inner and outer switchbox assembly that is relatively easy to fabricate.
It is a further object of the present invention to provide a novel inner and outer switchbox assembly and associated lever arm that is easy to access and maintain, and that requires a minimum of adjustment in the field.
These and other objects of the invention will be appreciated by reference to the summary of the invention and to the detailed description of the preferred embodiment that follow.